Fixed differential adjusting means for pressure sensitive electrical control devices



Jan. 12, 1954 W. E. BROWN FIXED DIFFERENTIAL ADJUSTING MEANS FORPRESSURE SENSITIVE ELECTRICAL CONTROL DEVICES iled Nov. 25, 1949 hl Mn 1c EQUAL. TO WEAR ALLOWANCE PLUS ARC GAP PLUS LEVER THICKNESS.

AME-m @(ibxww Patented Jan. 12, 1954 FIXED DIFFERENTIAL ADJUSTING MEANSFOR PRESSURE SENSITIVE ELECTRICAL CONTROL DEVICES William E. Brown,

Cutler-Hammer,

Pewaukee, Wis., assignor to Inc., Milwaukee, Wis., a corporation ofDelaware Application November 25, 1949, Serial N 0. 129,468

8 Claims.

This invention relates to pressure sensitive electrical control devicesand more particularly to a fixed differential adjusting means therefor.

As is well known, control devices of the aforementioned character aredesigned to open an electrical circuit at a predetermined pressure (ortemperature) and to reclose the circuit at a different predeterminedpressure (or temperature), the difference between the aforementionedpressures (or temperatures) being the differential of the controldevice.

In the known arts of manufacturing pressure sensitive electrical controldevices, the cumulation of manufacturing tolerances in the electricalcontrol assemblies renders it impractical to obtain a predeterminedfixed operating differential by means of close adherence to actualcontact spacing, contact pressure, and confined arc gap. Hence thedesired operating differential is usually obtained by fixing the arc gapto an approximat dimension and setting the differential by varying thewear allowance, or fixing the wear allowance and setting thedifferential by varying the arc gap. This necessitates pneumatic orthermostatic equipment for setting the differential. Moreover thedifferential is secured without providing for simultaneous control ofboth the amount of wear allowance and the size of the arc gap.

A primary objective of the present invention is to eliminate thaforementioned undesirable characteristics of prior devices of the typeunder consideration, and more particularly to provide in pressure (ortemperature) responsive electrical control devices means affordingaccurate and simultaneous predetermination of contact are gap, wearallowance, and differential.

'Another object is to achieve the aforementioned simultaneouspredetermination of all three factors through the medium of a singleadjusting member, which member may be extremely accurately and yetinexpensively and practically produced.

Another object is to provide in a control device of the aforementionedcharacter means for varying the ratio of contact are gap to contact wearallowance without changing the sum of those two factors and hencewithout affecting the differential of the device, thus permittingreestablishment of a desired contact wear allowance when the contactshave worn down without affecting the difierential of the device.

Another object is to provide means of the aforementioned characteraffording accurate simultaneous predetermination of differential,conmodifications may be made in the embodiment illustrated withoutdeparting from the spirit and scope of the appended claims.

In the drawings,

Figure l is a somewhat schematic view of a control device embodying theinvention, and

Fig. 2 is a side elevation of a fixed differential screw utilized in thecontrol device.

Referring first to Fig. 1, the reference numeral 5 denotes a pair ofspaced stationary contacts within a circuit (not shown) to be controlled, which contacts 5 are adapted to be.

bridged by a contactor 6 biased sition by a spring 1.

To effect movement of contactor 6 out of bridging engagement withcontacts 5 a snap acting system comprising pivoted levers or flippers 8and 9, and an over-center spring I!) connected therebetween is provided.Movement of said snap acting mechanism is in turn controlled by aconventional pressure (or temperature) responsive means shown ascomprising a bellows assembly ll, loading spring l2, and range adjustingmeans [3 comprising a screw [3 and a nonrotatable nut I3 As will beapparent, increased pressure in the bellows II will effect upwardmovement of the outer end of the flipper 9 connected thereto untilspring [0 goes through cen ter, thus effecting snap movement of lever 8to the dotted line position shown in Fig. 1, thus providing forcorresponding movement of contactor 6 into bridging engagement withcontacts 5, through the medium of spring I.

As previously pointed out, one of the objects of the present invention ithe provision of means for effecting an accurately predetermined fixeddifferential in electrical control devices of the character described.In the embodiment illustrated, the aforementioned means takes the formto the closed D0- of a fixed differential screw I4 which, as shown inFig. 2, has a peripheral groove 14 formed therein, by machining orotherwise, to provide spaced parallel surfaces M and 14.

Screw I4 is adapted for threading into the mounting plate l5 of thecontrol device in such relation to the aforementioned snap actingmechanism as to permit the free end of flipper 8 to oscillate upwardlyand downwardly within the limited space afforded by groove M of screwit. As best illustrated in Fig. 2, the spacing of surfaces 14* and {.4affording the limits to travel of the free end of lever B is calculatedto equal the desired contact wear allowance and are gap plus thethickness of lever B, such spacing being ac,- curately and inexpensivelyprovided in screw Id, as by machining or otherwise, and with tolerancesof .001 inch or less.

For example, if it were desired to have .032 inch wear allowance, .025inch arc gap, and the thickness of lever B were .030 inch, it would benecessary to machine or otherwise form groove M to .087 inch.

In assembling the control the threaded portion W of fixed differentialscrew it may be threaded into mounting plate i5 until lever 8 is forcedto just open the contacts. Screw it is then backed off enough to providethe desired predetermined wear allowance, for example, for a #8-32 screwthread, one full turn would give a desi ed wear allowance of .032 inch.Screw it may then be retained in this position by conventional retainingmeans, such as a non-rotatably supported frictional spring wire clip it.Since the total travel of lever Bis limited by groove f l to an exactmaximum adjusting the control for a predetermined wear allowanceprovides a definite'arc gap and simultaneously an accurately controlledand uniformly close predetermined differential for each control deviceproduced.

Moreover, the aforedescribed desired relation ship of screw 14 andflipper 8 having once been established, an enclosing casing ofconventional form (not shown) affording no access to screw I4, visual orotherwise, may be assembled to the control since no further adjustmentis necessary, the control having already been set with a knownpredetermined fixed differential and accurately predetermined contactwearallowance and arc gap. Thus utilization of pneumatic or thermostaticmeans is notnecessary to effect initial setting of the control device,nor are further adjust ments necessary to achieve such initial setting.

However, at such time as the contacts have worn down-to a pointwhere'the predetermined wear allowancehas been dissipated, the screw itmaybe-readjusted to reestablish the desired contact wear allowancewithout changing the dif-' ferential of the devi e, since the parallelsurfaces limiting travel of lever B will be moved siinultaneously inthesame direction and to the same degree, their relationship being fixed.

Lclaim:

.1. A- pressureresponsive electrical control de vice comprisinga setofcontacts, a pressure responsive operating element therefor, and meansaffording simultaneously a predetermined fixed operating differentialfor said device a contact arc gap andwear allowance the ratio ofwhich-maybe varied while the sum thereof remains constant, said meansaffording adjustability to reestablish a contact wear allowance tocompensate'for contact wear without affecting said-operatingdifferential and comprising integrally formed fixedly spaced, surfacesto limit.

travel of said operating element, and the spacing of-said surfaces beingequal to the sum of the desired wearallowance and are gap of saidcontacts plus the thickness of said operating element.-

:2. A pressure responsive electrical control device comprising a set ofelectrical contacts, a pressure responsive operating element therefor,and means affording simultaneously a predetermined fixed operatingdifferential for said device and predetermined total contact are gap andwear allowance, said means affording adjustability to reestablish acontact wearallowance to compensate for contact wear without affectingsaid operating differential and comprising a screw having a peripheralgroove of predetermined width forming a pair of integrally formedfixedly spaced parallel surfaces between which said operating element'isadapted to oscillate, said surfaces limiting the travel of saidoperating element, and the spacing of said surfaces being equal to thesum of the desired wear allowance and are gap of said contacts plus thethickness of said operating element.

3. in a pressure responsive electrical control device, a single meansaffording said device a predetermined fixedoperating differential andsimultaneously a predetermined total contact are gap and wear allowance,said means affording adjustability to reestablish a contact wearallowance .to

compensate for contact wear without affecting said operatingdifferential and comprising integrally formed fixedly spaced surfaceslimiting travel of an operating element of said device, the

spacing of said surfaces being equal to the sum of the desired contactwear allowance and arc gap plus the thickness of saidoperating element.

l. A pressure responsive electrical control device including anoperating element, and means affording said device adjustability toreestablish a desired contact wear allowance to compensate for contactwear without affecting a predetermined fixed operating differential forthe device,-

said means comprising integrally formed fixedly spaced parallel surfacesto limit travel ofsaid operating element and said surfaces being adjustable jointly while maintainingsaid fixedly spaced relation therebetween,thereby affording variation of the ratio between contact are gap andwear allowance but maintaining the sumthereof constant.

5. A wholly enclosed pressure responsive electrical control devicecomprising a set of contacts, a pressure responsiveoperating elementtherefor,

an enclosing casing for said device, and means aftegrally formed fixedlyspaced parallel surfaces between which said operating element-isadaptedto oscillate, said surfaces limiting travel of .said' element, and thespacingof said surfaces being equal to the sum of said predeterminedcontact wear allowance and are gap plus the thickness of said operatingelement.

6. A pressure responsive electrical control -de-' which may be variedwhilethe'sum thereof re-" mains constant, said means comprising fixedlyspaced surfaces to limit travel of the said 'opr ating element, and thespacing of said surfaces vice comprising a set of contacts, a pressurerebeing equal to the sum of the desired wear allowance and are gap ofsaid contacts, plus the thickness of said operating element.

7. A pressure responsive electrical control device comprising, a contactbiased for movement to a first position, an operating element for saidcontact having connection therewith to move said contact to a secondposition, and to release said contact for movement to said firstposition, and means affording simultaneously a predetermined fixedoperating differential for said device and a contact are gap and wearallowance, the ratio of which may 'be varied while the sum thereofremains constant, said means comprising fixedly spaced surfaces to limittravel of said operating element, and the spacing of said surfaces beingequal to the sum of the desired wear allowance and are gap of saidcontacts, plus the thickness of said operating element.

8. A pressure responsive electrical control device comprising, snapacting mechanism including a pressure responsive operating element and asnap acting element operated thereby, a contact connected for operationby said snap acting element and movable relative thereto, and meansaffording simultaneously a, predetermined fixed operating differentialfor said device and a contact arc gap and wear allowance, the ratio ofwhich may be varied while the sum thereof remains constant, said meanscomprising fixedly spaced surfaces to limit travel of said snap actingelement, and the spacing of said surfaces being equal to the sum of thedesired wear allowance and are gap of said contact plus the thickness ofsaid snap acting element.

WILLIAM E. BROWN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,092,559 Runaldue Sept. 7, 1937 2,193,127 Furnas et al Mar.12, 1940 2,194,533 Van Dyke Mar. 26, 1940 2,393,455 Beeman Jan. 22, 19462,437,846 Yeida Mar. 16, 1948 2,459,522 Grooms Jan. 18, 1949 2,548,877Dillman Apr. 17, 1951

